JAKARTA (Reuters) — Rival campaigners in Indonesia's elections next month are sparring over ways to fix the education system in Southeast Asia's biggest economy, which is widely blamed for failing to equip students with the skills to find jobs.

As a flood of young people enters the workforce, President Joko Widodo, who seeks re-election on April 17, has pledged to develop human capital in his second term, after focusing on roads, railways and airports since taking office in 2014.

In a vice-presidential debate this week, partly focused on education, opposition candidate Sandiaga Uno attacked Widodo's record and his signature program to improve one of the world's biggest vocational high school systems.

"How ironic it is that this country's economy is the world's 15th or 16th biggest, but faces difficulties providing jobs for its youth," Uno said, adding that Indonesia's vocational school graduates are the largest chunk of its 7 million unemployed.

Uno, who is running alongside retired general Prabowo Subianto, promised to cut youth unemployment by 2 million if elected.

Widodo and his running mate, cleric Ma'ruf Amin, have a double-digit lead in most opinion polls, but education could prove a weakness.

Indonesia should be enjoying a demographic sweet spot with its youthful population, but 90 per cent of its labor force of 131 million have no college degree and more than half works in informal sectors.

The World Bank said more than 55 per cent of citizens who complete education are functionally illiterate, far more than 14 per cent in neighboring Vietnam, which has been more successful in wooing manufacturers moving out of China.

The OECD ranks Indonesia's education system 62nd among the 72 nations in its Programme for International Student Assessment (PISA) that rates 15-year-olds' maths, science and reading skills. Neighboring Vietnam placed 8th.

Pledging to emulate Germany's skills training system, Widodo's government wants to spend $1.22 billion (all figures U.S.) in 2019 on improvements to 14,000 vocational schools which have 320,000 students, or more than double the past three years' spending.